This proposal is the third competitive renewal application for a Postdoctoral Research Training Program to support research in HIV/AIDS. The focus of this Program is investigation into clinically relevant pathogenesis of HIV/AIDS and associated illnesses. The overarching goal is to enable the most promising young investigators to identify and skillfully pursue avenues of basic science and translational HIV/AIDS research. The program is structured to train fellows with an MD degree, who have completed at least one year of clinical training in Infectious Diseases, as well as fellows with a PhD or DVM degree who wish to pursue postdoctoral studies in HIV/AIDS research. Two to three years of support for scientific training are requested depending on the prior research experience of particular individuals. The training program faculty represent a highly interactive and productive group of well-funded investigators who work at the interface between clinical and basic science investigations of HIV/AIDS and associated illnesses and is drawn from investigators in the Divisions of Geographic Medicine and Infectious Diseases and Clinical Care Research at Tufts-New England Medical Center and from the Departments of Pathology, Molecular Biology and Microbiology, Biochemistry, Pharmacology and Experimental Therapeutics and Public Health and Family Medicine and associated Graduate programs at the Tufts University School of Medicine and Tufts Sackler School of Graduate Biomedical Sciences and the Department of Biomedical Sciences at the Tufts Cummings School of Veterinary Medicine. These Departments and Programs, together with the Tufts-Brown Center for AIDS Research provide a rich academic environment in which MD and PhD fellows interact closely. This grant proposal is for support of five postdoctoral fellows per year. Each trainee works under the close supervision of faculty mentor/s and is supported by a Mentorship Committee. Academic enrichment includes required and elective didactic courses in bio-statistics, biochemistry, molecular microbiology, immunology, pharmacology, nutrition and clinical research. Attendance at a lecture series or course in the responsible conduct of research is mandatory for all fellows. Conferences include a research-in-progress conference, journal club, AIDS research and clinical conference and several invited speaker seminar series sponsored by the Center for AIDS research as well as the Graduate programs in Immunology, Molecular Microbiology, Pharmacology, Biochemistry and Clinical Research. The core of the program is supervised research under the guidance of well-funded faculty members with deep commitment to and experience in training future independent investigators in HIV/AIDS research.